The purpose of this project is to analyze the responses of bacteria to DNA damage in order to increase our understanding of the various mechanisms by which cells maintain the continuity of their genetic information. Our emphasis will be on the study of daughter strand gap repair (postreplication repair) in UV-irradiated cells of E. coli. Specifically, we will try to characterize some of the intermediates in daughter strand gap repair and determine whether the recA protein participates directly, or only indirectly, in this type of repair. In addition we will continue to examine the specificity and mechanism of action of endonuclease V of bacteriophage T4. Interpretation of experiments using this enzyme to study DNA repair requires an understanding of the relationship between its DNA-glycosylase activity and the associated AP endonuclease.